1. Field of the Invention
The present invention relates to a process for producing 2,3-dichlorobutadiene-1,3. More particularly, it relates to a process for producing 2,3-dichlorobutadiene-1,3 at high yield under the condition reducing a formation of polymerized products and reducing an amount of discharged organic materials of a solvent and chlorinated compounds in a drainage.
2. Description of the Prior Art
The process for producing 2,3-dichlorobutadiene-1,3 by a dehydrochlorination of 1,2,3-trichlorobutene-3 in a low boiling point water miscible polar solvent such as methanol in the presence of a base has been disclosed in (1) British Patent No. 946,014; and (2) Japanese Examined Patent Publication No. 6124/1978.
In the process (1), the reaction is carried out at ratios of methanol: sodium hydroxide: water of 75-90:10-5:15-5 by weight and at a molar ratio of sodium hydroxide to 1,2,3-trichlorobutene-3 of 0.7 to 1.0 at 40.degree.-100.degree. C. for a residence time of 3 minutes or shorter with stirring the mixture and the reaction mixture was stripped with steam and the vapor phase is cooled to recover 2,3-dichlorobutadiene-1,3 and the liquid phase is distilled to recover methanol. The conversion is in a range of 70 to 96% and the reaction yield is in a range of 82 to 87%. The reaction yield means a molar percent of the resulting 2,3-dichlorobutadiene-1,3 to the reacted 1,2,3-trichlorobutene-3.
In accordance with this process, the following disadvantages are found. The concentration of methanol should be high. The 2,3-dichlorobutadiene-1,3 polymer is easily formed by the heating in the step of stripping the reaction mixture with steam, to cause a short operation term. The conversion is low to remain a large amount of the unreacted 1,2,3-trichlorobutene-3. The reaction yield is not high. The drainage of the aqueous solution of sodium chloride contains a large amount of organic materials such as methanol and chlorinated compounds.
In the process (2), the reaction is continuously carried out at ratios of water miscible solvent:sodium hydroxide:water of 50-35:10-5:40-60 by weight and at a molar ratio of sodium hydroxide to 1,2,3-trichlorobutene-3 of 1.0 to 1.2 under the atmospheric pressure at 90.degree.-100.degree. C. The reaction mixture in the vapor phase is fed into a distillation column to separate the unreacted 1,2,3-trichlorobutene-3 and the solvent is extracted with water to recycle it into a reactor. The conversion is about 100% and the reaction yield is in a range of 88-91%.
In accordance with the process, the concentration of the solvent in the reaction mixture is not high and the conversion of 1,2,3-trichlorobutene-3 and the reaction yield are high. However, the following disadvantages are found. The reactor is heated at high temperature as 90.degree. to 100.degree. C. Excess alkali is remained because of the molar ratio of sodium hydroxide to 1,2,3-trichlorobutene-3 of more than 1. The polymer material causes fouling the reactor and plugging distillation column which results in short operation term as about 1 week. In order to prolong the life of the operation, it is necessary to reduce the molar ratio of the base or to decrease the reaction temperature. The contamination of the drainage with the unreacted 1,2,3-trichlorobutene-3 and the solvent is increased to reduce the yield and to increase the organic materials in the drainage.